WO1996012220A1

WO1996012220A1 - A temperature setting device

Info

Publication number: WO1996012220A1
Application number: PCT/SE1995/001187
Authority: WO
Inventors: Lennart W. Castwall; Christer C. I. Wiss
Original assignee: Ab Electrolux
Priority date: 1994-10-14
Filing date: 1995-10-13
Publication date: 1996-04-25
Also published as: SE9403519D0; AU3715195A

Abstract

There is described an individual-temperature control device for use with a cooking range (10) or like utility which includes one or more electrically heated zones (12, 14, 16, 18). A cooking vessel (42) can be placed on these zones. The temperature control device includes a sensor module (36) which is intended to be mounted on an associated attachment element (32) above the zones and cooking vessel respectively. The sensor module includes means (46) for aligning the module with a desired point (39) on the surface of foodstuff in the cooking vessel or with a desired point on the surface of liquid contained therein. The sensor module (36) functions to sense heat radiated from this point and is connected electrically to an electronic control unit (44). The control unit controls the temperature in the proximity of the point (39) in accordance with the sensed radiation, with the aid of a temperature control value stored in the control unit.

Description

A TEMPERATURE SETTING DEVICE

The present invention relates to a device for individual- temperature control. The device is intended for use in cooking ranges or like utilities that include one or more electrically heated zones on which a cooking vessel can be placed temporarily and selectively.

It is known to control the temperatures of the heating zones of cooking ranges with the aid of different types of tempera¬ ture setting devices by means of which the heating elements in said zones, for instance the heating filaments or heating spirals, can be set to a desired heating temperature.

The primary object of the present invention is to provide a considerable improvement with regard to controlling and maintaining the desired temperature of the actual cooking vessel or liquid contained therein. This object can be achieved with the aid of a device which includes a sensor module which is intended to be mounted on an associated attachment means located above said heating zones and said cooking vessel and which includes means for directing the module onto a desired point on the surface of the food being cooked in said vessel or onto a desired point on the surface of liquid contained in said vessel, wherein the sensor module functions to sense heat radiated from said point and is connected electrically to an electronic control unit which controls the temperature in the proximity of said point in response to the sensed radiation, through the medium of a temperature control value or set-point value stored in the control unit.

The novel temperature control device enables desired tempera¬ tures to be set and maintained with a high degree of preci- sion and in a simple and reliable manner. The power generated by a heating zone can also be controlled smoothly to a desired value, i.e. without abrupt changes in the heating process. This enables food to be prepared without overheating the food or scorching the cooking vessel .

Advantageous embodiments of the novel temperature control device for use with a cooking range or corresponding utility are set forth in the dependent Claims.

The invention will now be described in more detail with reference to the accompanying drawings, in which like components in the various Figures have been identified with like reference signs.

Fig. 1 is a front view in perspective of a conventional cooking range which includes an extraction fan and a novel , inventive temperature control device;

Fig. 2 is a block schematic which illustrates the positioning of the sensor module of the temperature control device in a system shown by way of example; and

Fig. 3 is a block schematic illustrating the various units in the sensor module and the components that coact therewith.

Fig. 1 is a simplified illustration of a cooking range 10 which includes four heating zones 12, 13, 16, 18 disposed in a conventional ceramic glass hob 20. Temperature setting devices 24, 26, 28, 30 are mounted on the front side 22 of the range 10.

An extraction fan 32 is mounted in a known manner above the range 10, at an approximate distance of 50 cm therefrom. In the illustrated case, the sensor module 36 of the novel temperature control device is mounted on the extraction fan 32 by means of a ball coupling suspension 34. The arrangement includes a guide lever 38 by means of which the sensor module 36 can be brought manually to a position of alignment with a given point. The sensor 40 in the module 36 can be directed onto a desired point 39, for instance towards an edge of a cooking vessel 42 or onto a point in liquid contained in said vessel placed on one of the heating zones 12, 14, 16, 18. An electronic control unit 44 forming part of the temperature control device is mounted in the immediate vicinity of the extraction fan 32 and connected to the sensor module. The control unit 44 functions to control the temperature that prevails at the aforesaid point 39 on the vessel 42 or on the liquid present therein in accordance with the radiation detected or sensed from said point, via a control value, or set-point value, stored in the control unit 44 and set with the aid of one of said temperature setting devices 24, 26, 28, 30. The electronic control unit 44 is preferably inte¬ grated with the extraction fan 32 so as not to have a detrimental effect on the total appearance of the range. Of course, the sensor module 36 shall also have a form which conforms with surrounding features of the range so as to blend therewith.

The device 46 by means of which the sensor module 36 is brought to a position of alignment with the desired detection point 39 may comprise a light-emitting means in the form of a laser pen or a lamp equipped with a light-directing lens (not shown). The arrangement is such that adjustment to the alignment device 46 to obtain a light spot at the position desired will also cause the sensor module 36 to be directed onto said spot.

Special advantages with regard to reliability in operation are obtained when the novel temperature control device is mounted in the direct vicinity of the extraction fan 32. For instance, when the sensor module is so positioned there can be generated in the vicinity of the sensor module 36 with the aid of the fan 32 an air flow which will prevent the device from being soiled with splashes of fat from a frying pan, for instance. In the case of an alternative sensor module mounting arrangement, for instance when the sensor module is mounted on a pivotal arm (not shown) , it may be necessary and advisable to protect the sensor module 36 with a cover plate which covers said module when the module is not in use.

Another advantage obtained when mounting the temperature control device in the vicinity of the extraction fan 32 is that immediate access can be had to the electrical low voltage part of the extraction fan 32.

The construction of the actual temperature control device and its manner of operation will now be described. In this regard, particular reference is made to an example of a suitable embodiment of a sensor module 36 and a control unit 44 included in the construction. The aligning device, however, is not dealt with in Figs. 2 and 3, since this device is known from constructions known in other contexts and may have many different designs.

The sensor module 36 illustrated in Fig. 2 is connected to the control unit 44 in which desired temperature values are set via a user interface. Output signals from the sensor module 36 are processed in the control unit 44 and control the power supply to the heating zone 18. The system is suitably designed so that the sensor module 36, the control unit 44 and the user interface 48 are activated with low voltage when the cooking range 10 is switched on. This has not been shown in the drawings.

Fig. 3 illustrates the individual components of the sensor module 36 in more detail. Thus, the illustrated sensor module 36 is an IR-type radiation sensor 40 which detects variations in radiation intensity through the medium of a switch 50. The switch 50 is designed to expose the radiation sensor 40 alternately to heat radiated from the desired point 39 on the cooking vessel and from a reference heat source 52 in the sensor module 36. The switch 50 may be of the kind that is operated by a magnetic circuit (not shown) whose pulse frequency is adapted so that the frequency of the intensity variation will be as low as possible in order to maximize sensitivity of the radiation sensor 40 and as high as possible in order to maximize its speed. The intensity of the IR radiation is amplitude-modulated with this frequency. This enables a simple and inexpensive radiation sensor 40 to be used. The demand placed on a measurement amplifier 51 connected downstream of the radiation sensor 40 is therewith low and the system response can be enhanced by phase-responsive detection of the measurement signal, for instance.

The radiation sensor 40 connected to the switch 50 may conveniently have the form of a temperature-compensated pyroelectric sensor. A sensor of this kind is used in IR- sensitive burglar alarm systems, among other things.

The output signal from the radiation sensor 40 is proportion- al to the variation in intensity between the radiation from the measuring point 39 and from the reference heat source 52. When the measuring point 39 and the reference heat source 52 radiate heat at the same intensity, the output signal from the radiation sensor will be zero. When the intensity is higher from the measuring point 39 than from the reference heat source, the output signal will be greater than zero in a given case when the measuring point is exposed and less than zero when the reference heat source 52 is exposed. The reverse applies when the reference heat source 52 is hotter. This applies to the illustrated embodiment, and can, of course, be reversed depending on design. It should be noted that the radiation sensor 40 does not take into account that the measuring point 39 and the reference heat source 52 may have different emissivities, i.e. that they absorb/reflect incident radiation with different efficiencies.

The radiation sensor 40 will preferably be temperature compensated, so that the output signal will not be influenced by slow variations in ambient temperature. The radiation sensor 40 has its greatest sensitivity at about 0.1 Hz in the case of this embodiment. Accordingly, the switching frequency is chosen to be as low as possible with regard to the desired speed, sensitivity (response) and disturbance immunity in relation to the mains frequency in the system.

In addition to the aforesaid components, the sensor module also includes a detector 54, a filter 56, an integrator 58 and a power stage 60. These components are connected in series between the amplifier 51 and the reference heat source 52. One output on the switch 50 is also connected directly to the detector 54. This is necessary for demodulation of the signal fed into the detector 50. The amplifier 51 connected between the radiation sensor 40 and the detector 54 functions to amplify the sensor output signal.

The signal obtained from the amplifier 51 is detected in the detector 55. Phase-responsive rectification is used to achieve maximum response in the system.

After passing through the filter 56, which suppresses undesirable frequency components generated by the detector 54, the detector output signal is roughly a d.c. voltage which is determined by the output signal from the radiation sensor 40. The detector extracts information relating to whether the measuring point 39 or the reference heat source 52 is the hottest. For instance, the reference heat source 52 is hotter than the measuring point 39 when a positive output signal is obtained, and vice versa. The measuring point 39 and the reference heat source 52 are equally as hot when a zero signal is obtained.

The integrator 58 connected downstream of the filter 56 functions to compare the filtered, detected signal with a control value. If the temperature of the measuring point 39 increases in relation to the value of the reference heat source 52, the integrator 58 forces the power stage 60 to increase the temperature of the source 52. If the temperature of the measuring point 39 decreases in relation to the value of the heat source 52, the integrator 58 forces the power stage 60 to lower the temperature of the reference heat source 52. The output signal from the integrator 58 is therewith set so that the temperature of the reference heat source 52 will follow the temperature of the measuring point 39. As shown in Fig. 3, the output of the integrator 58 may also be connected directly to the control unit 44. This allows the integrator output signal to be processed directly by the control unit 44.

Thus, the power stage 60 connected to the reference heat source 52 is used to convert the control voltage obtained from the integrator 58 to a current or voltage that can be used for the reference heat source 52. The reference heat source 52 may be comprised of a thermofoil. This may have a thickness of 25 μm.

The signal obtained from the sensor module 36 is generated by a temperature sensor (not shown) , suitably a thermoele¬ ment, which measures the temperature of the reference heat source 52. The thermosensor may be applied directly on the radiating surface of the reference heat source 52. This eliminates temperature gradients between temperature sensor measuring points and radiation sensor measuring points.

The sensor module 36 comprising the aforedescribed units may have the form of a feedback, phase-sensitive and zero- balanced measuring system for eliminating problems associated with temperature drifts, aging and deviations in component values. This design will provide a sensitive and accurate unit which is not influenced by normal component variations. The demands placed on these components are therefore small or moderate. The illustrated user interface 48 is intended to provide the control values and information concerning current settings of the control unit 44, this unit processing the information signals received from the sensor module 36 and controlling, adjusting, the temperature of the measuring point 39 in accordance with this information and in accordance with the working mode concerned.

It will be understood that the aforedescribed sensor module 36 can be modified. For instance, several of the components of the sensor module 36 can be designed in several different ways, such as the reference heat source 52 and the tempera¬ ture sensor.

Claims

1. A device for controlling the temperature of an individual electrically heated zone on a cooking range (10) that includes one or more such zones (12, 14, 16, 18) on which a cooking vessel (42) is placed temporarily and selectively, characterized in that the device includes a sensor module (36) which is intended to be mounted on an associated attachment means (36) above said zones anr? above said cooking vessel and which includes means (46) for αirecting the module onto a desired point (39) on the surface of the foodstuff in the cooking vessel or onto a desired point on the surface of liquid present in said vessel, wherein the sensor module (36) is also intended to sense heat radiated from said point and is electrically connected to an electronic control unit (44) which controls the temperature prevailing in the proximity of said point (39) in accordance with the sensed radiation, through the medium of a temperature control value stored in the control unit (44).

2. A device according to Claim 1, characterized in that the attachment element (32) is comprised of an extraction fan located above the range.

3. A device according to Claim 1, characterized in that the attachment element (32) is comprised of an attachment arm placed above the range.

4. A device according to any one of Claims l and 2, charac- terized in that the sensor module (36) is mounted on the attachment element by means of a ball joint suspension (34).

5. A device according to any one of Claims 1-4, character¬ ized in that the sensor module aligning device (46) includes an element for generating a light spot in the vicinity of the heat radiation point detected by the module.

6. A device according to Claim 5, characterized in that the sensor module alignment device (46) includes a module-mounted laser pen or like means which generates a red light spot in the proximity of the radiation point sensed by the module.

7. A device according to any one of Claims 1-6, character¬ ized in that the sensor module alignment device includes a lever (38) by means of which the module (36) can be brought manually into alignment with a desired sensing point (39).